I have a second spindle for my Dumore tool post grinder that I have never used. It is for small stones and ID grinding use. There are no markings with a model number apparent. My question is; does anyone know the thread size for mounting stones. The spindle has a short extension that has a fine ID thread. The thread is fine, and is too small for 5/16-24; and too big for 1/4-28? Did Dumore use a special size? Thanks fo any help.